The most important thing to get right with the cylinder and piston, is airseal. Ideally you’d achieve that by using compatible parts, either from the same brand or from brands/designers who work together, for example the Stalker piston is designed to work perfectly with the Novritsch SSG10 cylinders. If you end up with a mismatched combination, the piston wont seal fully to the inside of the cylinder and you’ll lose fps and consistency as air escapes.
Stock cylinders tend to be made from very cheap metals, will probably scrape and be quite rough when cocking, and won’t last. A good, solid steel cylinder is a very good upgrade and if you’re starting out with a cheap clone, is one that will need doing eventually. Teflon cylinders are very smooth when cycling, though I did note with mine that the trigger sear, being hardened steel, was wearing away the sides of the cylinder window. Another one to vote down, from experience, is the Maple Leaf “stainless steel” cylinder. I noticed when upgrading to Orange guide rings, that the new, tight guide rings wouldn’t fit down the length of the cylinder, only at the ends. What had happened, with use, is that the cylinder had expanded in the middle and warped out of shape. Being larger diameter throught the middle allowed air to escape past the piston and I suffered a drop in power and volume. I’s a problem I suspect many wouldn’t notice and I’ve not seen it documented anywhere else. Cylinders are pretty straightforward – just make sure it’s a good, strong material. Upgrading your guide rings is also a good idea if possible, and if not, it’s sometimes work polishing or sanding them (without taking too much material off) to smoothen the surface the cylinder rides on.
Pistons are more interesting. As a sniper obsessed with staying quiet and hidden, I’d always recommend an airbrake.
This pin on the end of a piston is slightly narrower than the hole in the cylinder head, and slots in when the piston slams forward. What this does with its blockage of the hole that the air escapes out of, is that it stops the piston just before impact, then slowly (some air still escapes through) finishes the travel. It forms an air cushion, rather than a flat slap of piston on cylinder head, making the gun quieter but at the expense of a few fps. Most pistons without however will rely on a rubberised pad to help dampen the noise.
Stock plastic pistons are very quiet indeed, but obviously more prone to wear and tear, and nobody seems to make any copies, though I’d love to be able to experiment with some for lower fps builds.
The other trend we’ve seen in recent years is the idea of a weighted piston, which is a very old idea off the sniper forums but recently has been latched onto and produced by various people. The idea is that by adding weight to the piston, the kinetic energy is increased, and the speed reduced. Without going too far into the details, increasing the weight allows for joule creep.
Joule creep is a controversial topic because it can be abused, and unfortunately I know a small handful of YouTubers who use joule creep to run hot guns and try to gain an advantage by cheating the chrono. What it allows is you to increase the power when running heavier bb’s. Imagine that your rifle runs at the limit on 0.20 (if you have a site that chronos on 0.20). When changing to heavier bb’s after chrono the joules increase, essentially adding extra power to the gun. Note that it isn’t the fps (feet per second = speed) but the energy in joules transferred that is increased. You can add weight yourself to any piston by adding weighted lead tape, usually used by golfers.
If used correctly, you can use a lighter spring at lower fps (quieter, easier bolt pull) and then when switching to heavier ammo, the power is increased to compensate for that loss in fps of the lighter spring. There are a couple of adjustable pistons now on the market, such as the Sniper Mechanic WASP and Stalker Scorpion, that allow you to adjust how much weight is added onto the piston (see scorpion review here), because too much weight means you start to lose power, as the spring isn’t strong enough to handle the extra weight. Initially when the WASP was released, I spoke to Sniper Mechanic and he explained that it wasn’t going to be suitable for every rifle build due to the different combinations of parts and other factors, but it was a tool to finely adjust some rifles. However, the market being what it is, many snipers now insist on weighted pistons. I would hope that they would be using them correctly and not to cheat chrono, but I suspect there are some out there looking to compensate for a skills gap by running hot (not that it helps them). They’re probably also the ones that go past the sweet spot and add as much weight on as possible too without understanding the ratios needed. Personally, I run both the WASP and the Scorpion, with the lightest weight possible, because quiet is good.
*Always make sure you keep piston o-rings well lubed with silicon grease, to stop them drying out, and to keep them flexible enough to maintain a good seal.